Mercurial VCS won't push to different branch

**Describe the bug**

I created new component, which is using mercurial VCS and supposed to pull from default branch and push translations to new branch. This doesn't work, "Push branch" option in Weblate is ignored and Weblate is always pushing to the default repository branch defined in Weblate as "Repository branch".

**To Reproduce**

Steps to reproduce the behavior:

1. Create any new repository with remote VCS containing at least 2 mercurial branches
2. Setup "Repository branch" as "default"
3. Setup "Push branch" as anything else than default
4. Translate/create a commit

**Expected behavior**

Weblate should follow the settings and pull from "Repository branch" and push to given "Push branch" in the settings, in case the push branch doesn't exist, it should create it with the push.

**Server configuration and status**

* Weblate: 4.2.2
* Mercurial: 4.8.2